Communication control device, communication control method, terminal device, program, and communication control system

ABSTRACT

Provided is a communication control device that controls radio communication conducted by a terminal device according to a time-division duplex (TDD) scheme on a radio communication network, the communication control device including a configuration section that configures, for each frame that includes a plurality of subframes, a link direction configuration expressing a link direction per subframe for the radio communication. The configuration section configures a timing of control signaling in a second link direction which is associated with data transmission in a first link direction in the radio communication, and which is opposite to the first link direction, independently of the configured link direction configuration.

TECHNICAL FIELD

The present disclosure relates to a communication control device, acommunication control method, a terminal device, a program, and acommunication control system.

BACKGROUND ART

Recently, a high-speed cellular radio communication scheme called LongTerm Evolution (LTE) is being practically implemented. The LTE scheme iscategorized into the FD-LTE scheme and the TD-LTE scheme, on the basisof differences in the duplex scheme. The FD-LTE scheme adoptsfrequency-division duplex (FDD) as the duplexing scheme, with the uplinkand the downlink being operated on mutually different frequency bands.The TD-LTE scheme adopts time-division duplex (TDD) as the duplexingscheme, with the uplink and the downlink being operated on the samefrequency band. Both the FD-LTE scheme and the TD-LTE scheme use a frameformat in which one radio frame (having a duration of 10 ms) is made upof 10 subframes each having a duration of 1 ms. In the FD-LTE scheme,the link direction does not change over time on the same frequency band,whereas in the TD-LTE scheme, the link direction may change persubframe.

In the TD-LTE scheme, a set of link directions per subframe for eachradio frame (that is, a combination of the link directions of 10subframes) is designated the link direction configuration (or the UL-DLconfiguration). According to Non-Patent Literature 1, seven types oflink direction configurations from Configuration 0 to Configuration 6are defined. A radio base station (designated eNB in the LTE scheme)signals to a terminal device (designated UE in the LTE scheme) bybroadcasting the link direction configuration configured for each radioframe in a system information block type 1 (SIB1). In the currentstandard specification, the update cycle of the link directionconfiguration conducted using the SIB1 is 640 ms. Non-Patent Literature2 proposes shortening this cycle to 320 ms.

In the case of updating the link direction configuration on a shortcycle, a problem arises in that link direction collisions frequentlyoccur between the two link direction configurations pre-update andpost-update, as described in Non-Patent Literature 3. Link directioncollisions cause loss in data transmission and control signaling at thetimings when a collision occurs, lowering communication throughput.Non-Patent Literature 3 describes two cases in which link directioncollisions may invite lowered throughput: the case of an acknowledgement(ACK) and a negative acknowledgement (NACK) of a downlink transmission,and the case of an uplink grant (UL grant) preceding an uplinktransmission. As a solution to this problem, Non-Patent Literature 3proposes a technique that dynamically modifies the ACK/NACK or uplinkgrant timing in the case of determining that a link direction collisionhas occurred.

CITATION LIST Non-Patent Literature

-   Non-Patent Literature 1: 3GPP TS 36.211 V10.0.0 (2010-12)”, Dec. 22,    2010-   Non-Patent Literature 2: “Semi-static reconfiguration of TDD UL-DL    configuration”, R1-122266, 3GPP TSG RAN WG1 Meeting #69, Prague,    Czech Republic, May 21-25, 2012-   Non-Patent Literature 3: “Discussion on HARQ and UL-grant timing    with dynamic TDD UL-DL configuration”, R1-121260, 3GPP TSG RAN WG1    Meeting #68bis, Jeju, Korea, Mar. 26-30, 2012

SUMMARY OF INVENTION Technical Problem

However, according to the technique proposed by Non-Patent Literature 3,a link direction collision determination and a control signaling timingmodification will be executed every time the link directionconfiguration is updated. If one presupposes that the link directionconfiguration is updated on a short cycle, such a solution significantlywould increase the processing load on the terminal device and the basestation.

Consequently, it is desirable to provide an improved mechanism capableof preventing lowered throughput caused by link direction collisionswith a lower processing load under conditions in which the linkdirection configuration is updated on a short cycle.

Solution to Problem

According to the present disclosure, there is provided a communicationcontrol device that controls radio communication conducted by a terminaldevice according to a time-division duplex (TDD) scheme on a radiocommunication network, the communication control device including aconfiguration section that configures, for each frame that includes aplurality of subframes, a link direction configuration expressing a linkdirection per subframe for the radio communication. The configurationsection configures a timing of control signaling in a second linkdirection which is associated with data transmission in a first linkdirection in the radio communication, and which is opposite to the firstlink direction, independently of the configured link directionconfiguration.

According to the present disclosure, there is provided a communicationcontrol method for controlling radio communication conducted by aterminal device according to a time-division duplex (TDD) scheme on aradio communication network, the communication control method includingconfiguring, for each frame that includes a plurality of subframes, alink direction configuration expressing a link direction per subframefor the radio communication, and configuring a timing of controlsignaling in a second link direction which is associated with datatransmission in a first link direction in the radio communication, andwhich is opposite to the first link direction, independently of theconfigured link direction configuration.

According to the present disclosure, there is provided a program causinga computer of a communication control device that controls radiocommunication conducted by a terminal device according to atime-division duplex (TDD) scheme on a radio communication network tofunction as a configuration section that configures, for each frame thatincludes a plurality of subframes, a link direction configurationexpressing a link direction per subframe for the radio communication.The configuration section configures a timing of control signaling in asecond link direction which is associated with data transmission in afirst link direction in the radio communication, and which is oppositeto the first link direction, independently of the configured linkdirection configuration.

According to the present disclosure, there is provided a terminal deviceincluding a radio communication section that communicates with a basestation according to a time-division duplex (TDD) scheme, and a controlsection that, according to a link direction configuration indicated byfirst signaling from the base station, configures a link direction persubframe for each frame that includes a plurality of subframes. Thecontrol section configures, on the basis of second signaling from thebase station, an offset between a timing of a data transmission in afirst link direction and a timing of control signaling in a second linkdirection which is associated with the data transmission, and which isopposite to the first link direction.

According to the present disclosure, there is provided a radiocommunication method executed by a terminal device provided with a radiocommunication section that communicates with a base station according toa time-division duplex (TDD) scheme, the radio communication methodincluding configuring, according to a link direction configurationindicated by first signaling from the base station, a link direction persubframe for each frame that includes a plurality of subframes, andconfiguring, on the basis of second signaling from the base station, anoffset between a timing of a data transmission in a first link directionand a timing of control signaling in a second link direction which isassociated with the data transmission, and which is opposite to thefirst link direction.

According to the present disclosure, there is provided a program causinga computer of a terminal device provided with a radio communicationsection that communicates with a base station according to atime-division duplex (TDD) scheme to function as a control section that,according to a link direction configuration indicated by first signalingfrom the base station, configures a link direction per subframe for eachframe that includes a plurality of subframes. The control sectionconfigures, on the basis of second signaling from the base station, anoffset between a timing of a data transmission in a first link directionand a timing of control signaling in a second link direction which isassociated with the data transmission, and which is opposite to thefirst link direction.

According to the present disclosure, there is provided a communicationcontrol system including a terminal device that communicates with a basestation according to a time-division duplex (TDD) scheme, and acommunication control device that controls radio communication conductedby the terminal device, the communication control device including aconfiguration section that configures, for each frame that includes aplurality of subframes, a link direction configuration expressing a linkdirection per subframe for the radio communication. The configurationsection configures a timing of control signaling in a second linkdirection which is associated with data transmission in a first linkdirection in the radio communication, and which is opposite to the firstlink direction, independently of the configured link directionconfiguration.

Advantageous Effects of Invention

According to technology in accordance with the present disclosure, it ispossible to prevent lowered throughput caused by link directioncollisions with a lower processing load under conditions in which thelink direction configuration is updated on a short cycle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram for describing an example of a linkdirection configuration in TD-LTE.

FIG. 2 is an explanatory diagram illustrating a list of configurablelink direction configurations in TD-LTE.

FIG. 3A is a first explanatory diagram for describing the configurationof a link direction configuration according to buffer status.

FIG. 3B is a second explanatory diagram for describing the configurationof a link direction configuration according to buffer status.

FIG. 4 is an explanatory diagram for describing signaling of a linkdirection configuration using a new message.

FIG. 5 is an explanatory diagram for describing a first case in whichthroughput may be lowered due to a link direction collision.

FIG. 6 is an explanatory diagram for describing a second case in whichthroughput may be lowered due to a link direction collision.

FIG. 7A is an explanatory diagram illustrating a first example of asubframe that includes a cell-specific reference symbol (CRS).

FIG. 7B is an explanatory diagram illustrating a second example of asubframe that includes a CRS.

FIG. 8 is an explanatory diagram illustrating an example of aconfiguration of a communication control system according to anembodiment.

FIG. 9A is an explanatory diagram for describing a first example of newsignaling.

FIG. 9B is an explanatory diagram for describing a second example of newsignaling.

FIG. 9C is an explanatory diagram for describing a third example of newsignaling.

FIG. 10A is an explanatory diagram for describing a first example of anew ACK/NACK transmission timing.

FIG. 10B is an explanatory diagram for describing a second example of anew ACK/NACK transmission timing.

FIG. 11A is an explanatory diagram for describing a first example of anew UL grant transmission timing.

FIG. 11B is an explanatory diagram for describing a second example of anew UL grant transmission timing.

FIG. 12 is a block diagram illustrating an exemplary configuration of acommunication control device according to an embodiment.

FIG. 13 is a block diagram illustrating an example of a configuration ofa dynamic TDD terminal according to an embodiment.

FIG. 14A is the first half of a sequence diagram illustrating an exampleof the flow of a process that may be executed in an embodiment.

FIG. 14B is the second half of a sequence diagram illustrating anexample of the flow of a process that may be executed in an embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the drawings, elements that have substantiallythe same function and structure are denoted with the same referencesigns, and repeated explanation is omitted.

Also, the description will proceed in the following order.

1. Overview

-   -   1-1. Configuring link direction configuration    -   1-2. Signaling link direction configuration    -   1-3. Link direction collision    -   1-4. Additional issues

2. Configuration of communication control system

-   -   2-1. Overview of system    -   2-2. Basic principles    -   2-3. Exemplary configuration of communication control device    -   2-4. Exemplary configuration of dynamic TDD terminal    -   3. Example of process flow

4. Conclusion

1. OVERVIEW

[1-1. Configuring Link Direction Configuration]

FIG. 1 is an explanatory diagram for describing an example of a linkdirection configuration in TD-LTE. Referring to FIG. 1, a frame formatof a radio frame adopted in the LTE scheme is illustrated. One radioframe includes 10 subframes (#0 to #9). The duration of each subframe is1 ms, and the duration of one radio frame is 10 ms. The link directionis configured per subframe. In the example of FIG. 1, the link directionof subframes labeled “D” is downlink, and such subframes are designateddownlink subframes. The link direction of subframes labeled “U” isuplink, and such subframes are designated uplink subframes. Thesubframes labeled “S” are special subframes unique to TD-LTE. Asexemplified in FIG. 1, a downlink signal transmitted from a base station(eNB) arrives at a terminal device (UE) with a delay dT. The terminaldevice takes the delay dT of an uplink signal arriving at the basestation into consideration, and transmits an uplink signal prior to thetiming of an uplink subframe of the base station. A special subframe isinserted at the timing of switching from a downlink subframe to anuplink subframe, and acts as a buffer period so that the timings ofreceiving a downlink signal and transmitting an uplink signal at aterminal device do not overlap. A special subframe includes a downlinkpilot time slot in which a downlink signal is received by the UE, aguard period, and an uplink pilot time slot in which an uplink signal istransmitted by the UE. Note that downlink data may also be transmittedfrom the base station to the terminal device in the special subframe. Inthis sense, the special subframe may be viewed as being a type ofdownlink subframe.

FIG. 2 illustrates a list of seven types of configurable link directionconfigurations in TD-LTE, which are defined in Non-Patent Literature 1.As FIG. 2 demonstrates, the 0th subframe (#0) and the 5th subframe (#5)are configured as downlink subframes in all configurations. The 1stsubframe (#1) is configured as a special subframe in all configurations.The 2nd subframe (#2) is configured as an uplink subframe in allconfigurations. Configuration of the remaining subframes differs foreach configuration.

On the right edge of FIG. 2, the ratio of the number of uplink subframesversus the number of downlink subframes (UL-DL ratio) is indicated. InConfiguration 0, there are six uplink subframes and two downlinksubframes, for a UL-DL ratio of 6:2. In Configuration 1, there are fouruplink subframes and four downlink subframes, for a UL-DL ratio of 4:4.In Configuration 2, there are two uplink subframes and six downlinksubframes, for a UL-DL ratio of 2:6. In Configuration 3, there are threeuplink subframes and six downlink subframes, for a UL-DL ratio of 3:6.In Configuration 4, there are two uplink subframes and seven downlinksubframes, for a UL-DL ratio of 2:7. In Configuration 5, there is oneuplink subframe and eight downlink subframes, for a UL-DL ratio of 1:8.In Configuration 6, there are five uplink subframes and three downlinksubframes, for a UL-DL ratio of 5:3.

A radio communication system that operates according to the TD-LTEscheme may decide which of the seven types of link directionconfigurations to use on the basis of the UL-DL traffic ratio.Generally, an uplink signal is buffered by the terminal device's uplinkbuffer before transmission is granted. Meanwhile, a downlink signal isbuffered by the PDN Gateway (P-GW) on the core network beforetransmission is scheduled. If the amount of buffered traffic exceeds thebuffer capacity, a buffer overflow occurs. In addition, traffic that hasbeen buffered past a designated period may be discarded as a timeout.Accordingly, the terminal device periodically transmits to the basestation a buffer status report indicating the amount of uplink trafficbeing buffered. The P-GW provides buffer signaling that indicates theamount of downlink traffic being buffered. Consequently, a schedulerinside the base station or another control node is able to compute theUL-DL traffic ratio for each cell. For example, in the example of FIG.3A, there is more buffered uplink traffic than buffered downlinktraffic. In this case, by configuring a link direction configurationwith a high uplink ratio, the buffered uplink traffic may be decreased.On the other hand, in the example of FIG. 3B, there is more buffereddownlink traffic than buffered uplink traffic. In this case, byconfiguring a link direction configuration with a high downlink ratio,the buffered downlink traffic may be decreased.

[1-2. Signaling Link Direction Configuration]

A link direction configuration that has been configured by the basestation or another control node is signaled with a broadcast using theSIB1 from the base station to the terminal device. The update cycle ofthe SIB1 in the current standard specification is 640 ms. According tothe above Non-Patent Literature 2, the update cycle of the linkdirection configuration using the SIB1 may be shortened to 320 ms. TheSIB1 is one of various types of system information blocks (SIBs) mappedto the downlink shared channel (DL-SCH). A message transporting an SIBis designated a system information (SI) message. The shortesttransmission cycle of an SI message is 80 ms. Consequently, as long asthe link direction configuration is signaled with an SI message, theshortest update cycle of the link direction configuration is 80 ms.

Recently, radio communication traffic has been dramatically increasing.The UL-DL traffic ratio varies frequently. Consequently, the signalingcycle of the link direction configuration in existing techniques is lessthan sufficient to track the variations in the UL-DL traffic ratio. Ifthe link direction configuration updates do not keep up with thevariations in the UL-DL traffic ratio, the amount of buffered trafficwill increase, leading to decreased resource utilization and loweredthroughput. Without taking signaling overhead into account, since theduration of one radio frame is 10 ms, the ideal update cycle of the linkdirection configuration is 10 ms. However, if the mechanism forsignaling the link direction configuration is completely changed fromexisting techniques, existing terminal devices will be unable to acquirethe link direction configuration and become inoperative.

Accordingly, in an embodiment, there is introduced a new messagedifferent from a SI message for signaling the link directionconfiguration to a terminal device on a shorter cycle than existingtechniques. In this specification, this new message to be introduced isdesignated the dynamic configuration (DC) message. In addition, aterminal device that receives only an SI message in order to configurethe link direction configuration is designated a legacy terminal (legacyUE). In contrast, a terminal device that receives a DC message isdesignated a dynamic TDD terminal (dynamic TDD UE).

FIG. 4 is an explanatory diagram for describing signaling of a linkdirection configuration using a DC message.

The top part of FIG. 4 illustrates how a legacy terminal periodicallyreceives an SI message transporting the SIB1 on a cycle C1. The SIB1includes a link direction configuration identity (one of theconfiguration numbers 0 to 6 exemplified in FIG. 2) configured for thelegacy terminal at that time. Following this link directionconfiguration, the legacy terminal configures the link direction of itsown radio communication circuit per subframe. The SI message signalingcycle C1 is 320 ms, for example. At this point, suppose that the UL-DLtraffic ratio varies greatly at a time 20 ms after receiving the SImessage. In this case, a mismatch between the configured link directionconfiguration and the UL-DL traffic ratio would continue over a periodof 300 ms until the next SI message is received.

The bottom part of FIG. 4 illustrates how a dynamic TDD terminalperiodically receives a DC message on a cycle C2 (where C2<C1). The DCmessage includes a link direction configuration identity (one of theconfiguration numbers 0 to 6 exemplified in FIG. 2) configured for thedynamic TDD terminal at that time. Following this link directionconfiguration, the dynamic TDD terminal configures the link direction ofits own radio communication circuit per subframe. The DC messagesignaling cycle C2 may be an integer multiple of 10 ms. For example, ifthe signaling cycle C2=40 ms, the period of a continued mismatch betweenthe link direction configuration and the UL-DL traffic ratio would be atworst 40 ms.

In an embodiment, the base station signals to a legacy terminal a firstlink direction configuration using an SI message, and signals to adynamic TDD terminal a second link direction configuration using a DCmessage. In this specification, the first link direction configurationthat may be updated on the cycle C1 is designated the legacyconfiguration. Also, the second link direction configuration isdesignated the dynamic TDD configuration. The base station signals thesetwo configurations, but in actual practice operates according to thedynamic TDD configuration as described later. Note that when adesignated event occurs, such as a dynamic TDD terminal establishing anew connection or returning to active mode, the base station may alsotransmit a DC message without waiting for the signaling cycle to elapse.

In another embodiment, the signaling to a legacy terminal using an SImessage may also be omitted. Technology according to the presentdisclosure is also applicable to a system which contains no legacyterminals for which backward compatibility should be guaranteed, andwhich signals only a dynamic TDD configuration that may be updated on ashort cycle.

[1-3. Link Direction Collision]

In the case of updating the dynamic TDD configuration on a short cycle,link direction collisions may occur frequently between the twoconfigurations pre-update and post-update. Herein, a link directioncollision refers to a mutual difference between the link direction ofthe ith subframe (where i=0, . . . , 9) of a radio frame before anupdate and the link direction of the ith subframe of a radio frame afteran update. Link direction collisions cause loss in data transmission andcontrol signaling at the timings when a collision occurs, loweringcommunication throughput. Hereinafter, the two cases described inNon-Patent Literature 3 will be described.

(1) ACK/NACK in Response to Downlink Transmission

The acknowledgement (ACK) and negative acknowledgement (NACK) are thebasic control signaling that form the base of the hybrid automaticrepeat request (HARQ), a mechanism for ensuring the reliability of datatransmission. The offset between the timing of a downlink transmissionand the timing of an ACK/NACK is defined for each link directionconfiguration in Table 10.1.3.1-1 of 3GPP TS 36.213 (see Table 1).

TABLE 1 Offset between downlink transmission and ACK/NACK (See 3GPP TS36.213 Table 10.1.3.1-1) UL-DL Subframe n Configuration 0 1 2 3 4 5 6 78 9 0 — — 6 — 4 — — 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, 4, 6 —— — — 8, 7, — — 4, 6 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 7,11 6, 5, — — — — — — 4, 7 5 — — 13, 12, 9, 8, 7, 5, — — — — — — — 4, 11,6 6 — — 7 7 5 — — 7 7 —

Table 1 illustrates timing offsets between a downlink transmission andan ACK/NACK associated with that downlink transmission, in units ofnumbers of subframes. The transmission timing of an ACK/NACK will bedescribed while also referencing FIG. 5. The top part of FIG. 5illustrates two consecutive radio frames F11 and F12 configured withConfiguration 3. In the radio frames F11 and F12, downlink transmissionmay occur in the 0th, 1st, 5th, 6th, 7th, 8th, and 9th subframes.Referring to the Configuration 3 row in Table 1, an ACK/NACK in responseto a downlink transmission in the 0th subframe may be transmitted in the4th subframe indicating an offset of 4. An ACK/NACK in response to adownlink transmission in the 1st subframe may be transmitted in the 2ndsubframe (of the next radio frame) indicating an offset of 11. AnACK/NACK in response to a downlink transmission in the 5th subframe maybe transmitted in the 2nd subframe (of the next radio frame) indicatingan offset of 7. An ACK/NACK in response to a downlink transmission inthe 6th subframe may be transmitted in the 2nd subframe (of the nextradio frame) indicating an offset of 6. An ACK/NACK in response to adownlink transmission in the 7th subframe may be transmitted in the 3rdsubframe (of the next radio frame) indicating an offset of 6. AnACK/NACK in response to a downlink transmission in the 8th subframe maybe transmitted in the 3rd subframe (of the next radio frame) indicatingan offset of 5. An ACK/NACK in response to a downlink transmission inthe 9th subframe may be transmitted in the 4th subframe (of the nextradio frame) indicating an offset of 5. The correspondence relationshipsof such timings are indicated by the dashed arrows in FIG. 5. A deviceparticipating in radio communication stores a standardized table likeTable 1 in advance, and may decide on a transmission timing of anACK/NACK in response to a downlink transmission by referencing thattable.

However, in the case in which the link direction configuration isupdated, there exist subframes with different link directions betweenthe pre-update radio frame and the post-update radio frame. In thebottom part of FIG. 5, Configuration 2 is configured for a radio frameF22 that follows a radio frame F21 configured with Configuration 3. Inthis case, link direction collisions occur at the 3rd and 4th subframes.As a result, an ACK/NACK in response to a downlink transmission in the7th, 8th, and 9th subframes of the radio frame F21 as well as the 0thsubframe of the radio frame F22 cannot be transmitted by the terminaldevice in the 3rd and 4th subframes of the radio frame F22 as specifiedby the above table. If the ACK/NACK is lost, even if the correspondingdownlink transmission was conducted normally, the base station is unableto recognize this fact, and may resend already-transmitted data.Consequently, radio resources may be wasted, and system throughput maybe lowered.

(2) UL Grant Preceding Uplink Transmission

An uplink grant (UL grant) is control signaling for informing theterminal device that uplink transmission has been scheduled. The timingoffset between an uplink transmission and an uplink grant is defined foreach link direction configuration in Table 8-2 of 3GPP TS 36.213 (seeTable 2).

TABLE 2 Offset between UL grant and uplink transmission (See 3GPP TS36.213 Table 8-2) TDD UL/DL subframe number n Configuration 0 1 2 3 4 56 7 8 9 0 4 6, 7 4 6, 7 1 6 4 6 4 2 4 4 3 4 4 4 4 4 4 5 4 6 7 7 7 7 5

Table 2 illustrates timing offsets between an uplink transmission and aUL grant associated with that uplink transmission, in units of numbersof subframes. Note that whereas Table 1 illustrates offsets goingbackwards (in the past) with reference to the transmission timing of anACK/NACK, Table 2 illustrates offsets going forwards (in the future)with reference to the transmission timing of a UL grant. Thetransmission timing of a UL grant will be described while alsoreferencing FIG. 6. The top part of FIG. 6 illustrates two consecutiveradio frames F31 and F32 configured with Configuration 4. In the radioframes F31 and F32, uplink transmission may occur in the 2nd and 3rdsubframes. Referring to the Configuration 4 row in Table 2, a UL grantfor an uplink transmission in the 2nd subframe may be transmitted in the8th subframe (of the previous radio frame) indicating an offset of 4. AUL grant for an uplink transmission in the 3rd subframe may betransmitted in the 9nd subframe (of the previous radio frame) indicatingan offset of 4. The correspondence relationships of such timings areindicated by the dashed arrows in FIG. 6. A device participating inradio communication stores a standardized table like Table 2 in advance,and may decide on a transmission timing of a UL grant for an uplinktransmission by referencing that table.

However, in the case in which the link direction configuration isupdated, there exist subframes with different link directions betweenthe pre-update radio frame and the post-update radio frame. In thebottom part of FIG. 6, Configuration 4 is configured for a radio frameF42 that follows a radio frame F41 configured with Configuration 0. Inthis case, link direction collisions occur at the 4th, 7th, 8th, and 9thsubframes. As a result, a UL grant for an uplink transmission in the 2ndand 3rd subframes of the radio frame F42 cannot be transmitted by thebase station in the 8th and 9th subframes of the radio frame F41 asspecified by the above table. The terminal device will not executeuplink transmission unless a UL grant is transmitted. In this case,since the 2nd and 3rd subframes of the radio frame F42 become unused,the radio resource utilization falls, and system throughput may belowered.

(3) Problems of Existing Techniques

Non-Patent Literature 3 proposes several solutions to the issuesdiscussed above under conditions in which the link directionconfiguration is updated on a short cycle. These solutions involvedelaying or moving up the timings of control signaling (ACK/NACK or ULgrant) or the like, and all require a link direction collision judgmentand individual modification of the timings of control signaling. If onepresupposes that the link direction configuration is updated on a shortcycle, such solutions, in addition to significantly increasing theprocessing load and worsening power consumption, also have the demeritof inviting cost increases due to complicated implementation. Technologyin accordance with the present disclosure proposes an improved mechanismthat, while avoiding these demerits, makes it possible to preventlowered throughput caused by link direction collisions with a lowerprocessing load under conditions in which the link directionconfiguration is updated on a short cycle.

[1-4. Additional Issues]

Note that as a result of the dynamic TDD configuration being updated ona shorter cycle than the legacy configuration, link direction collisionsmay also occur between these two configurations. There is also apossibility that link direction collisions between the twoconfigurations may affect the synchronization operation of legacyterminals.

Generally the synchronization operation of a terminal device includesbasic synchronization and synchronization tracking. Basicsynchronization refers to synchronization from a state in which theoperating timings of the terminal device are completely unsynchronizedwith the operating timings of the base station. Basic synchronization isconducted by having the terminal device search for a primarysynchronization signal (PSS) and a secondary synchronization signal(SSS). Via basic synchronization, the terminal device acquires the cellID of the connecting cell, and ascertains the rough timings of radioframes. Synchronization tracking is executed after the completion ofbasic synchronization in order to improve the synchronization precision.Synchronization tracking is conducted by having the terminal devicereceive a cell-specific reference symbol (CRS). As exemplified in FIG.7A, as a general rule the CRS is dispersively inserted into the physicaldownlink control channel (PDCCH) and the physical downlink sharedchannel (PDSCH) of each downlink subframe. The terminal device maintainsthe synchronization of operating timings by receiving the CRS in thesedownlink subframes in both idle mode (RRC_Idle) and active mode(RRC_Connected), irrespective of whether or not data addressed to thedevice itself exists. Note that if a downlink subframe is configured asan MBMS single frequency network (MBSFN) subframe, the PDSCH of thatdownlink subframe is used only for the purpose of broadcasting ormulticasting a Multimedia Broadcast Multicast Services (MBMS) signal. Asexemplified in FIG. 7B, the CRS is not inserted into the PDSCH of anMBSFN subframe.

At this point, assume that Configuration 2 is configured as the legacyconfiguration, and Configuration 4 is configured as the dynamic TDDconfiguration, for example (see FIG. 2). Since the base station operatesin accordance with the dynamic TDD configuration, the link direction ofthe 3rd subframe (#3) is uplink, and the link direction of the 7thsubframe (#7) is downlink. However, a legacy terminal, following thelegacy configuration, recognizes that the link direction of the 3rdsubframe is downlink, and the link direction of the 7th subframe isuplink. Subsequently, the legacy terminal attempts to receive the CRSfor synchronization tracking in the 3rd subframe. However, the basestation does not transmit the CRS in that subframe, which is actually anuplink subframe. As a result, there occurs a risk of loweredsynchronization tracking precision in the legacy terminal. Note that inthe 7th subframe, although the base station transmits the CRS, thelegacy terminal does not receive that CRS. However, the synchronizationtracking precision of the legacy terminal does not drop even if some ofthe CRS symbols are not received, and thus the effects of link directioncollision in the 7th subframe are small.

According to the embodiment described in the next section, the effectsof link direction collision between the two configurations may beavoided or mitigated.

2. CONFIGURATION OF COMMUNICATION CONTROL SYSTEM

[2-1. Overview of System]

FIG. 8 is an explanatory diagram illustrating an example of aconfiguration of a communication control system 1 according to anembodiment of technology in accordance with the present disclosure.Referring to FIG. 8, the communication control system 1 includes a basestation 100. The base station (eNB) 100 provides radio communicationservice in accordance with the TD-LTE scheme to a legacy terminal 104and a dynamic TDD terminal 200 positioned inside a cell 102. The basestation 100 is connected to a core network 106, typically realized asthe Evolved Packet Core (EPC). The core network 106 includes variouscontrol nodes, such as the Mobility Management Entity (MME), the ServingGateway (S-GW), and the P-GW, for example.

The legacy terminal 104 is a terminal device that operates according toa legacy configuration. The dynamic TDD terminal 200 is a terminaldevice capable of operating according to a dynamic TDD configuration.The dynamic TDD terminal 200 may also be capable of additionallyoperating according to a legacy configuration. The control function thatconfigures these link direction configurations and conducts controlsignaling for the terminal devices may be placed in the base station100, or any control node that communicates with these terminal devicesvia the base station 100. As an example, the following descriptionassumes that the base station 100 includes this control function.

[2-2. Basic Principles]

This section describes the basic principles for preventing loweredthroughput caused by link direction collisions while still enabling thedynamic TDD configuration to be updated on a short cycle in thecommunication control system 1.

(1) Introduction of New Signaling

In the present embodiment, the base station 100 configures a legacyconfiguration for the legacy terminal 104. In addition, the base station100 configures a dynamic TDD configuration for the dynamic TDD terminal200. The dynamic TDD configuration is updatable on a shorter timeinterval than the signaling cycle of the legacy configuration.Furthermore, the base station 100 configures the timings of controlsignaling in a second link direction (UL or DL) that is associated withdata transmission in a first link direction (DL or UL), independently ofthe dynamic TDD configuration. The control signaling referred to hereinmay include one or both of an ACK/NACK associated with a downlinktransmission, and a UL grant associated with an uplink transmission. Thebase station 100 then executes several types of signaling on the basisof these configurations.

FIG. 9A is an explanatory diagram for describing a first example of newsignaling that may be introduced in the present embodiment. Referring toFIG. 9A, the base station 100 executes a signaling SIG0 directed towardsthe legacy terminal 104, as well as a signaling SIG1 and a signalingSIG2 directed towards the dynamic TDD terminal 200. For example, thesignaling SIG0 is an SI message informing the legacy terminal 104 of thelegacy configuration. The signaling SIG1 is a dynamic configuration (DC)message informing the dynamic TDD terminal 200 of the dynamic TDDconfiguration. The signaling SIG2 is a new message informing the dynamicTDD terminal 200 of the transmission timing of an ACK/NACK associatedwith a downlink transmission. The dynamic TDD terminal 200, on the basisof the received signaling SIG2, recognizes the offset between thedownlink subframe in which the downlink transmission is conducted andthe uplink subframe in which to transmit the ACK/NACK.

FIG. 9B is an explanatory diagram for describing a second example of newsignaling that may be introduced in the present embodiment. Referring toFIG. 9B, the base station 100 executes a signaling SIG0 directed towardsthe legacy terminal 104, as well as a signaling SIG1 and a signalingSIG3 directed towards the dynamic TDD terminal 200. For example, thesignaling SIG3 is a new message informing the dynamic TDD terminal 200of the transmission timing of an uplink transmission associated with aUL grant. The dynamic TDD terminal 200, on the basis of the signalingSIG3, recognizes the offset between the downlink subframe in which theUL grant is received and the uplink subframe in which uplinktransmission is granted.

FIG. 9C is an explanatory diagram for describing a third example of newsignaling that may be introduced in the present embodiment. Referring toFIG. 9C, the base station 100 executes a signaling SIG0 directed towardsthe legacy terminal 104, as well as a signaling SIG1, a signaling SIG2,and a signaling SIG3 directed towards the dynamic TDD terminal 200.

In all of the examples in FIGS. 9A to 9C, it is sufficient to transmitthe signaling SIG2 and SIG3 to the dynamic TDD terminal 200 just once,insofar as the timings of the control signaling are not modified. Thetrigger for the signaling SIG2 and SIG3 may be, for example, the dynamicTDD terminal 200 establishing a new connection to the base station 100(including handover from another system), or the dynamic TDD terminal200 returning from idle mode to active mode.

(2) Signaled Values (SIG0)

In the present embodiment, in each of the signaling SIG0 to SIG3, thebase station 100 respectively specifies one from among a set ofconfiguration candidates. The set of configuration candidates typicallymay include Configuration 0 to Configuration 6 exemplified in FIG. 2.The set of configuration candidates may be unique to the radiocommunication network, and in this case, some link directionconfigurations may be excluded from the set of configuration candidates.

In the signaling SIG0, typically a configuration candidate with a higheruplink ratio may be specified as the legacy configuration. For example,in the case in which Configuration 0 having the highest uplink ratio isspecified as the legacy configuration, the legacy terminal 104recognizes the 0th and 5th subframes as downlink subframes. Furthermore,the 0th and 5th subframe are maintained as downlink subframes, even ifthe base station 100 operates according to any of the otherconfigurations. Consequently, the base station 100 transmits the CRS insubframes in which the legacy terminal 104 attempts to receive the CRS,thereby guaranteeing that the legacy terminal 104 will conductsynchronization tracking normally.

(3) Signaled Values (SIG1)

In the signaling SIG1, a configuration candidate selected according tothe ratio between the uplink traffic and the downlink traffic on thenetwork (the UL-DL traffic ratio) is specified as the dynamic TDDconfiguration. For example, in the case in which the set ofconfiguration candidates includes Configuration 0 to Configuration 2,Configuration 0 may be specified when the ratio of uplink traffic ishigher. In the same case, Configuration 2 may be specified when theratio of downlink traffic is higher. In the same case, Configuration 1may be specified when there is little difference between the ratio ofuplink traffic and the ratio of downlink traffic. Monitoring of theUL-DL traffic ratio may be conducted on a time interval ranging from oneto several radio frames (that is, from 10 ms to several tens ofmilliseconds), for example. The dynamic TDD configuration may also beselected on the basis of a prediction of a future UL-DL traffic ratio.

(4) Signaled Values (SIG2)

As discussed above, the signaling SIG2 informs the dynamic TDD terminal200 of the transmission timing of an ACK/NACK associated with a downlinktransmission. In the signaling SIG2, the base station 100 may specify acandidate with a higher downlink ratio from among the set ofconfiguration candidates. Particularly, the signaling SIG2 preferablyspecifies a configuration candidate in which all subframes at positionsthat may become downlink subframes in other configuration candidates aredefined as downlink subframes. For example, in the case in which the setof configuration candidates includes Configuration 0 to Configuration 6,the signaling SIG2 may specify Configuration 5.

FIG. 10A is an explanatory diagram for describing a first example of anew ACK/NACK transmission timing based on the signaling SIG2. In theexample of FIG. 10A, the top part presupposes that Configuration 5 hasbeen specified in the signaling SIG2. Meanwhile, the bottom part of FIG.10A illustrates a radio frame F51 and the following radio frame F52. Thedynamic TDD configuration configured in the radio frame F51 isConfiguration 3. The dynamic TDD configuration configured in the radioframe F52 is Configuration 2. In this case, link direction collisionsoccur at the 3th, 4th, and 7th subframes. However, referring to theConfiguration 5 row in Table 1, an ACK/NACK in response to a downlinktransmission in any downlink subframe is transmitted in the 2ndsubframe. Specifically, as indicated by the dashed arrows in the bottompart of FIG. 10A, an ACK/NACK in response to a downlink transmission inthe 1st, 5th, 6th, 7th, and 8th downlink subframes of the radio frameF51 is transmitted in the 2nd uplink subframe of the radio frame F52. AnACK/NACK in response to a downlink transmission in the 9th downlinksubframe of the radio frame F51 is transmitted in the 2nd uplinksubframe of the next radio frame after the radio frame F52. An ACK/NACKin response to a downlink transmission in the 0th downlink subframe ofthe radio frame F52 is transmitted in the 2nd uplink subframe of thenext radio frame after the radio frame F52. In addition, since linkdirection collisions do not occur in the uplink subframes in which theseACK/NACKs are transmitted, ACK/NACK loss caused by link directioncollision is avoided.

FIG. 10B is an explanatory diagram for describing a second example of anew ACK/NACK transmission timing based on the signaling SIG2. In theexample of FIG. 10B, the top part presupposes that Configuration 4 hasbeen specified in the signaling SIG2. Meanwhile, the bottom part of FIG.10B illustrates a radio frame F61 and the following radio frame F62. Thedynamic TDD configuration configured in the radio frame F61 isConfiguration 3. The dynamic TDD configuration configured in the radioframe F62 is Configuration 1. In this case, link direction collisionsoccur at the 4th, 7th, and 8th subframes. However, referring to theConfiguration 4 row in Table 1, an ACK/NACK in response to a downlinktransmission in any downlink subframe is transmitted in the 2nd or 3rdsubframe. Specifically, as indicated by the dashed arrows in the bottompart of FIG. 10B, an ACK/NACK in response to a downlink transmission inthe 1st and 5th downlink subframes of the radio frame F61 is transmittedin the 2nd uplink subframe of the radio frame F62. An ACK/NACK inresponse to a downlink transmission in the 6th, 7th, 8th, and 9thdownlink subframes of the radio frame F61 is transmitted in the 3rduplink subframe of the radio frame F62. An ACK/NACK in response to adownlink transmission in the 0th downlink subframe of the radio frameF62 is transmitted in the 2nd uplink subframe of the next radio frameafter the radio frame F62. In addition, since link direction collisionsdo not occur in the uplink subframes in which these ACK/NACKs aretransmitted, ACK/NACK loss caused by link direction collision isavoided. The example of FIG. 10B is effective in the case in whichConfiguration 5 or the like is excluded from the set of configurationcandidates.

In this way, by deciding the ACK/NACK transmission timing on the basisof a specific configuration that may be signaled separately from thedynamic TDD configuration, it is possible to avoid ACK/NACK loss causedby link direction collision, and prevent lowered system throughput.

Note that the legacy terminal 104 does not receive the signaling SIG2,and operates according to the legacy configuration specified in thesignaling SIG0 (Configuration 0, for example). Referring to theConfiguration 0 row in Table 1, an ACK/NACK in response to a downlinktransmission in the 6th subframe is transmitted in the 2nd subframe,which is an uplink subframe. Accordingly, by restricting scheduling sothat a downlink transmission to the legacy terminal 104 is scheduled inthe 6th subframe, the base station 100 is able to suitably receive anACK/NACK in response to that downlink transmission.

(5) Signaled Values (SIG3)

As discussed above, the signaling SIG3 informs the dynamic TDD terminal200 of the transmission timing of an uplink transmission associated witha UL grant. In the signaling SIG3, the base station 100 may specify acandidate with a higher uplink ratio from among the set of configurationcandidates. Particularly, the signaling SIG3 preferably specifies aconfiguration candidate in which all subframes at positions that maybecome uplink subframes in other configuration candidates are defined asuplink subframes. For example, in the case in which the set ofconfiguration candidates includes Configuration 0 to Configuration 6,the signaling SIG3 may specify Configuration 0.

FIG. 11A is an explanatory diagram for describing a first example of anew UL grant transmission timing based on the signaling SIG3. In theexample of FIG. 11A, the top part presupposes that Configuration 0 hasbeen specified in the signaling SIG3. Meanwhile, the bottom part of FIG.11A illustrates a radio frame F71 and the following radio frame F72. Thedynamic TDD configuration configured in the radio frame F71 isConfiguration 0. The dynamic TDD configuration configured in the radioframe F72 is Configuration 4. In this case, link direction collisionsoccur at the 4th, 7th, 8th, and 9th subframes. However, referring to theConfiguration 0 row in Table 2, a UL grant for an uplink transmission inany uplink subframe is transmitted in the 0th, 1st, 5th, or 6thsubframe. The link direction of these four subframes is always downlink,irrespective of configuration. Specifically, as indicated by the dashedarrows in the bottom part of FIG. 11A, a UL grant for an uplinktransmission in the 2nd and 3rd uplink subframes of the radio frame F72is transmitted in the 6th downlink subframe of the radio frame F71. Linkdirection collisions do not occur in this downlink subframe in which aUL grant is transmitted.

FIG. 11B is an explanatory diagram for describing a second example of anew UL grant transmission timing based on the signaling SIG3. In theexample of FIG. 11B, the top part presupposes that Configuration 6 hasbeen specified in the signaling SIG3. Meanwhile, the bottom part of FIG.11B illustrates a radio frame F81 and the following radio frame F82. Thedynamic TDD configuration configured in the radio frame F81 isConfiguration 1. The dynamic TDD configuration configured in the radioframe F82 is Configuration 3. In this case, link direction collisionsoccur at the 4th, 7th, and 8th subframes. However, referring to theConfiguration 6 row in Table 2, and as indicated by the dashed arrows inthe bottom part of FIG. 11B, a UL grant for an uplink transmission inthe 2nd uplink subframe of the radio frame F82 is transmitted in the 5thdownlink subframe of the radio frame F81. A UL grant for an uplinktransmission in the 3rd uplink subframe of the radio frame F82 istransmitted in the 6th downlink subframe of the radio frame F81. A ULgrant for an uplink transmission in the 4rd uplink subframe of the radioframe F82 is transmitted in the 9th downlink subframe of the radio frameF81. Link direction collisions do not occur in these downlink subframesin which a UL grant is transmitted. The example of FIG. 11B is effectivein the case in which Configuration 0 or the like is excluded from theset of configuration candidates.

In this way, by deciding the UL grant transmission timing on the basisof a specific configuration that may be signaled separately from thedynamic TDD configuration, it is possible to avoid producing subframesthat may go unused for uplink transmission, and prevent lowered systemthroughput.

Note that the legacy terminal 104 does not receive the signaling SIG3,and operates according to the legacy configuration specified in thesignaling SIG0 (Configuration 0, for example). Referring to theConfiguration 0 row in Table 2, a UL grant for an uplink transmission inany uplink subframe is transmitted in the 0th, 1st, 5th, or 6thsubframe, which are always downlink subframes. Consequently, the basestation 100 is able to suitably transmit a UL grant to the legacyterminal 104, without imposing special constraints on the scheduling ofuplink transmissions from the legacy terminal 104.

Specific exemplary configurations of the communication control device(in the present embodiment, the base station 100) and the dynamic TDDterminal 200 implementing the basic principles described in this sectionwill be described in the following sections.

[2-3. Exemplary Configuration of Communication Control Device]

In the present embodiment, the base station 100 acts as a communicationcontrol device that controls radio communication conducted by a terminaldevice according to a time-division duplex (TDD) scheme. FIG. 12 is ablock diagram illustrating an example of a configuration of the basestation 100. Referring to FIG. 12, the base station 100 is equipped witha radio communication section 110, a signal processing section 120, aninterface section 130, a configuration section 140, a storage section142, and a signaling section 150.

(1) Radio Communication Section

The radio communication section 110 is a communication interface fortransmitting and receiving radio signals between the base station 100and one or more terminal devices. The radio communication section 110includes one or more antennas (not illustrated) and an RF circuit. Theradio communication section 110 receives an uplink signal transmittedfrom a terminal device, and conducts amplification, frequencyconversion, and AD conversion of the received signal. In addition, theradio communication section 110 conducts DA conversion, frequencyconversion, and amplification of a signal to be transmitted, andtransmits a downlink signal to a terminal device.

An uplink signal received by the radio communication section 110includes an uplink data signal and uplink signaling. The uplinksignaling includes a buffer status report from each terminal device, aswell as an ACK/NACK associated with a downlink transmission. Inaddition, a downlink signal transmitted by the radio communicationsection 110 includes a downlink data signal and downlink signaling. Thedownlink signaling may include a UL grant associated with an uplinktransmission, as well as the signaling SIG0, SIG1, SIG2, and SIG3discussed earlier.

(2) Signal Processing Section

The signal processing section 120 includes a signal processing circuitfor conducting equalization, demodulation, and decoding of a receivedsignal input from the radio communication section 110, as well asencoding and modulation of a signal to be transmitted that is output tothe radio communication section 110. The signal processing section 120outputs data included in a demodulated and decoded received signal tothe interface section 130. Also, the signal processing section 120encodes and modulates a signal to be transmitted that includes datainput from the interface section 130.

(3) Interface Section

The interface section 130 includes an interface group such as the X2interface by which the base station 100 communicates with other basestations, and the S1 interface by which the base station 100communicates with a control node on the core network 106. Eachcommunication interface in the interface section 130 may be a wiredcommunication interface or a wireless communication interface. Theinterface section 130 receives buffer signaling from a P-GW, forexample. Such buffer signaling indicates the traffic amount of buffereddownlink data signals for each terminal device. The interface section130 outputs received buffer signaling to the configuration section 140.

(4) Configuration Section

The configuration section 140 configures, for each frame that includesmultiple subframes, a link direction configuration expressing a linkdirection per subframe for the purpose of radio communication inside thecell. More specifically, the configuration section 140 configures alegacy configuration for a first terminal group that includes one ormore legacy terminals 104. In addition, the configuration section 140configures a dynamic TDD configuration for a second terminal group thatincludes one or more dynamic TDD terminals 200. The radio communicationsection 110 operates according to a dynamic TDD configuration configuredby the configuration section 140.

For example, the configuration section 140 may semi-permanentlyconfigure a predefined link direction configuration (Configuration 0,for example) as the legacy configuration. The link directionconfiguration configured as the legacy configuration may be defined soas to ensure normal synchronization tracking using the CRS by the legacyterminal 104.

In addition, the configuration section 140, on the basis of the mostrecent value or a predicted future value of the UL-DL traffic ratio,selects a dynamic TDD configuration to configure for each radio framefrom among multiple configuration candidates. For example, if moreuplink traffic is being buffered, the configuration section 140 mayselect a link direction configuration with a higher uplink ratio.Similarly, if more downlink traffic is being buffered, the configurationsection 140 may select a link direction configuration with a higherdownlink ratio. The set of configuration candidates that may be selectedon a radio communication network may be all of the seven types of linkdirection configurations defined in Non-Patent Literature 1, or a subsetunique to the network.

In addition, the configuration section 140 configures the timings ofcontrol signaling in a second link direction which is associated withdata transmission in a first link direction of radio communication witha terminal device, and which is the opposite of the first linkdirection, independently of the configured dynamic TDD configuration.The control signaling referred to herein includes one or both of anACK/NACK transmitted from a terminal device as a response to a downlinktransmission, and a UL grant transmitted to a terminal device prior toan uplink transmission. In the present embodiment, the configurationsection 140 configures the timings of the control signaling in a formatthat specifies one from among selectable configuration candidates.

For example, the configuration section 140 may specify a candidate witha higher downlink ratio from among the set of configuration candidatesas the timing of an ACK/NACK in response to a downlink transmission. Asa result, as described using FIGS. 10A and 10B, it is possible to avoidproducing link direction collisions in uplink subframes in which anACK/NACK is transmitted, even when the dynamic TDD configuration isupdated. Both the base station 100 and the dynamic TDD terminal 200store in advance a table that associates downlink transmission timingsand ACK/NACK timings for each configuration candidate (see Table 1).Subsequently, the timing at which the dynamic TDD terminal 200 actuallytransmits an ACK/NACK is decided on the basis of an entry in that tablecorresponding to the configuration configured by the configurationsection 140.

Additionally, the configuration section 140 may specify a candidate witha higher uplink ratio from among the set of configuration candidates asthe timing of a UL grant preceding an uplink transmission. As a result,as described using FIGS. 11A and 11B, it is possible to decide a ULgrant timing while avoiding producing subframes that go unused foruplink transmission, even when the dynamic TDD configuration is updated.Both the base station 100 and the dynamic TDD terminal 200 store inadvance a table that associates uplink transmission timings and UL granttimings for each configuration candidate (see Table 2). Subsequently,the timing at which the radio communication section 110 actuallytransmits a UL grant is decided on the basis of an entry in that tablecorresponding to the configuration configured by the configurationsection 140.

The storage section 142 is a storage medium that stores variousparameters configured by the configuration section 140, as well asvarious data referenced when configuring these parameters. For example,the storage section 142 stores in advance a set of configurationcandidates selectable by the base station 100. In addition, the storagesection 142 stores a legacy configuration and a dynamic TDDconfiguration configured by the configuration section 140. In addition,the storage section 142 stores in advance a first table that associatesdownlink transmission timings and ACK/NACK timings, and a second tablethat associates uplink transmission timings and UL grant timings. Inaddition, the storage section 142 stores ACK/NACK timings and UL granttimings configured by the configuration section 140 in a format thatspecifies a configuration candidate number.

In the present embodiment, the configuration section 140 also acts as ascheduler. More specifically, the configuration section 140 schedulesdownlink transmissions from the base station 100 to each terminaldevice, and uplink transmissions from each terminal device to the basestation 100. Furthermore, the configuration section 140 generatesdownlink assignments and uplink grants (UL grants) that indicate thescheduling results. Scheduling information is transmitted to eachterminal device by the signaling section 150. The transmission timing ofa UL grant is decided from the timing of a scheduled uplink transmissionby referencing the entry of the configuration number specified for thepurpose of UL grant timing inside the second table stored by the storagesection 142.

(5) Signaling Section

The signaling section 150 signals a link direction configurationconfigured by the configuration section 140, and the timings of thecontrol signaling discussed earlier (one or both of an ACK/NACK and a ULgrant), to a terminal device via the radio communication section 110.

More specifically, on a signaling cycle C1, the signaling section 150signals to the legacy terminal 104 a legacy configuration bybroadcasting an SI message (SIG0). Also, on a signaling cycle C2 that isshorter than the signaling cycle C1, the signaling section 150 signalsto the dynamic TDD terminal 200 a dynamic TDD configuration bytransmitting a DC message (SIG1). At timings when the link directionconfiguration is not updated, transmission of an SI message or a DCmessage may be skipped.

Also, in the present embodiment, the signaling section 150 signals tothe dynamic TDD terminal 200 the timing of an ACK/NACK in response to adownlink transmission by specifying a configuration number configured bythe configuration section 140 (SIG2). Additionally, the signalingsection 150 signals to the dynamic TDD terminal 200 the timing of a ULgrant by specifying a configuration number configured by theconfiguration section 140 (SIG3). The signaling section 150 may alsoexecute this signaling when the dynamic TDD terminal 200 connects to thebase station 100 (which may include both establishing a new connectionand returning to active mode). Additionally, the signaling section 150may also execute this signaling periodically.

[2-4. Exemplary Configuration of Dynamic TDD Terminal]

FIG. 13 is a block diagram illustrating an exemplary configuration of adynamic TDD terminal 200 according to the present embodiment. Referringto FIG. 13, the dynamic TDD terminal 200 is equipped with a radiocommunication section 210, a signal processing section 220, a controlsection 230, and a storage section 240.

(1) Radio Communication Section

The radio communication section 210 is a communication interface fortransmitting and receiving radio signals between the dynamic TDDterminal 200 and the base station 100. The radio communication section210 includes one or more antennas (not illustrated) and an RF circuit.The radio communication section 210 receives a downlink signaltransmitted from the base station 100, and conducts amplification,frequency conversion, and AD conversion of the received signal. Inaddition, the radio communication section 210 conducts DA conversion,frequency conversion, and amplification of a signal to be transmitted,and transmits an uplink signal to the base station 100.

A downlink signal received by the radio communication section 210includes a downlink data signal and downlink signaling. The downlinksignaling may include a UL grant associated with an uplink transmission,as well as the signaling SIG1, SIG2, and SIG3 discussed earlier. Also,an uplink signal transmitted by the radio communication section 210includes an uplink data signal and uplink signaling. The uplinksignaling includes a buffer status report, as well as an ACK/NACKassociated with a downlink transmission.

(2) Signal Processing Section

The signal processing section 220 includes a signal processing circuitfor conducting equalization, demodulation, and decoding of a receivedsignal input from the radio communication section 210, as well asencoding and modulation of a signal to be transmitted that is output tothe radio communication section 210. The signal processing section 220is connected to a processor (not illustrated) that realizes processingin a higher layer, for example. The signal processing section 220 thenoutputs data included in a demodulated and decoded received signal to ahigher layer. Also, the signal processing section 220 encodes andmodulates a signal to be transmitted that includes data input from ahigher layer.

(3) Control Section

The control section 230 controls radio communication by the dynamic TDDterminal 200 according to the TD-LTE scheme. For example, the controlsection 230 configures link directions per subframe in the radiocommunication section 210 and the signal processing section 220according to a dynamic TDD configuration specified in a DC messagereceived from the base station 100. In addition, in a downlink subframe,the control section 230 causes the radio communication section 210 toreceive the CRS and execute synchronization tracking. Also, the controlsection 230 periodically generates a buffer status report indicating thetraffic amount of buffered uplink data signals, and transmits thegenerated buffer status report from the radio communication section 210to the base station 100.

In addition, the control section 230 configures, on the basis ofsignaling from the base station 100, an offset between the timing ofdata transmission in a first link direction, and the timing of controlsignaling in a second link direction associated with that datatransmission.

More specifically, the control section 230 configures, on the basis ofthe signaling SIG2 received from the base station 100, a timing offsetbetween a downlink transmission and an ACK/NACK associated with thatdownlink transmission. The offset configured at this point is indicatedby an entry specified by the signaling SIG2 in a first table thatassociates downlink transmission timings and ACK/NACK timings. Thecontrol section 230 then causes the radio communication section 210 toreceive a downlink transmission according to a downlink assignmentreceived by the radio communication section 210. Furthermore, thecontrol section 230 decides individual ACK/NACK timings on the basis ofthe configured offset and downlink transmission timings. Subframes thatcorrespond to an ACK/NACK timing decided in this way all become uplinksubframes, irrespective of the dynamic TDD configuration. Consequently,the control section 230 does not have to make a link direction collisionjudgment for every downlink transmission, and operations that delay anACK/NACK are also unnecessary.

Also, the control section 230 configures, on the basis of the signalingSIG3 received from the base station 100, a timing offset between anuplink transmission and a UL grant associated with that uplinktransmission. The offset configured at this point is indicated by anentry specified by the signaling SIG3 in a second table that associatesuplink transmission timings and UL grant timings. The control section230 then causes the radio communication section 210 to transmit anuplink transmission according to a UL grant received by the radiocommunication section 210. There is a possibility that the timing of anuplink transmission may also correspond to one of the uplink subframesin the configured dynamic TDD configuration. In other words, since anuplink subframe with no possibility of being used does not exist,lowered radio resource utilization is avoided.

(4) Storage Section

The storage section 240 is a storage medium that stores data andprograms used in order for the control section 230 to control radiocommunication by the dynamic TDD terminal 200. For example, the storagesection 240 stores a dynamic TDD configuration configured by the controlsection 230. In addition, the storage section 240 stores in advance afirst table that associates downlink transmission timings and ACK/NACKtimings, and a second table that associates uplink transmission timingsand UL grant timings. In addition, the storage section 240 storesACK/NACK timings and UL grant timings configured by the control section230 in a format that specifies a configuration candidate number.

(5) Dual Mode Support

Note that the dynamic TDD terminal 200 may also be capable of operatingin both a first operating mode that configures link directions accordingto a legacy configuration similarly to a legacy terminal 104, and asecond operating mode that configures link directions according to adynamic TDD configuration on a shorter cycle. For example, the dynamicTDD terminal 200 may operate in the first operating mode during thestage of initial synchronization with a radio communication network, andafterwards transition to the second operating mode in response toreceiving a DC message. According to such a configuration, afterreliably establishing synchronization with the base station 100according to an existing procedure, the dynamic TDD terminal 200 is ableto flexibly exchange signaling with the base station 100 on variouschannels, and acquire a configuration for the second operating mode.Additionally, the dynamic TDD terminal 200 may infrequently receive anSI message (that is, the first operating mode) in idle mode (RRC_Idle),and frequently receive a DC message (that is, the second operating mode)in active mode (RRC_(—) Connected). As a result, a rise in powerconsumption while in idle mode may be avoided.

3. PROCESS FLOW EXAMPLE

FIGS. 14A and 14B are sequence diagrams illustrating an example of theflow of a process that may be executed in a communication control system1 according to the present embodiment. Note that a base station 100, alegacy terminal 104, and a dynamic TDD terminal 200 participate in theprocess described herein. As an example, the dynamic TDD terminal 200 isassumed to be a terminal that supports the dual mode discussed above.

Referring to FIG. 14A, first, the base station 100 periodicallybroadcasts an SI message on a signaling cycle C1 (step S100). The SImessage is a message that signals a legacy configuration, and specifiesConfiguration 0, for example. The legacy terminal 104 receives the SImessage, and specifies Configuration 0 as the legacy configuration. Thedynamic TDD terminal 200 likewise receives the SI message, andestablishes initial synchronization with the base station 100 accordingto the legacy configuration (step S104).

The base station 100 collects data on the amount of uplink trafficbuffered in the terminal devices and the amount of downlink trafficbuffered on the core network, and monitors the UL-DL traffic ratio (stepS108). Subsequently, the base station 100 configures a dynamic TDDconfiguration according to (the most recent value of, or a predictedfuture value of) the UL-DL traffic ratio (step S112).

The dynamic TDD terminal 200, having established initial synchronizationwith the base station 100, transmits a connection request to the basestation 100 in an uplink subframe (step S116). The base station 100accepts the connection from the dynamic TDD terminal 200 (step S120).

Next, the base station 100 transmits a capability query to the dynamicTDD terminal 200 (step S124). In response to receiving the query, thedynamic TDD terminal 200 responds to the base station 100, indicatingthat the device itself supports dynamic TDD (receiving the signalingSIG1, SIG2, and SIG3) (step S128).

Next, the base station 100 transmits a DC message to the dynamic TDDterminal 200 (step S132). The DC message is a message signaling adynamic TDD configuration, and indicates the configuration numberconfigured by the base station 100 in step S112. Herein, assume that theDC message also serves as the signaling SIG2 and SIG3, in addition tothe signaling SIG1. In other words, the DC message specifies aconfiguration number for the timing of an ACK/NACK in response to adownlink transmission, as well as a configuration number for the timingof a UL grant. In the example of FIG. 14A, the dynamic TDD configurationis Configuration 2, the ACK/NACK timing is Configuration 5, and the ULgrant timing is Configuration 0.

The dynamic TDD terminal 200, upon receiving the DC message from thebase station 100 in step S132, replies with a response (step S136), andmodifies the link direction configuration to the dynamic TDDconfiguration, that is, Configuration 2 (step S140). In addition, thedynamic TDD terminal 200 respectively stores Configuration 5 as theACK/NACK timing, and Configuration 0 as the UL grant timing.

After that, if traffic for the dynamic TDD terminal 200 is produced, thebase station 100 schedules the traffic (step S144). If the producedtraffic is downlink traffic, the base station 100 transmits the downlinktraffic to the dynamic TDD terminal 200 according to a downlinkassignment (step S148). The dynamic TDD terminal 200 decides thetransmission timing of an ACK/NACK in response to the downlink trafficon the basis of the configuration number signaled from the base station100 in step S140 (Configuration 5), and transmits an ACK/NACK to thebase station 100 at the decided timing (step S152).

On the other hand, if the produced traffic is uplink traffic, the basestation 100 decides the transmission timing of a UL grant from thetiming of an uplink transmission on the basis of the configurationnumber signaling to the dynamic TDD terminal 200 in step S140(Configuration 0), and transmits a UL grant to the dynamic TDD terminal200 at the decided timing (step S148). The dynamic TDD terminal 200decides the timing of an uplink transmission for the UL grant on thebasis of the configuration number signaled from the base station 100,and transmits uplink traffic to the base station 100 at the decidedtiming (step S152).

The sequence proceeds to FIG. 14B. Subsequently, suppose that the basestation 100 detects variation in the UL-DL traffic ratio (step S160). Atthis point, the base station 100 decides to update the configuration ofthe dynamic TDD configuration according to the UL-DL traffic ratio. Thebase station 100 then transmits a DC message to the dynamic TDD terminal200 (step S164). The dynamic TDD terminal 200 replies with a response(step S168). The DC message transmitted at this point is a messagesignaling the dynamic TDD configuration after a future update (in theexample of FIG. 14B, Configuration 3).

Furthermore, suppose that before the dynamic TDD configuration isupdated, traffic for the dynamic TDD terminal 200 is produced again. Atthis point, the base station 100 schedules the traffic (step S172). Thebase station 100 then transmits downlink traffic or a UL grant to thedynamic TDD terminal 200 (step S176).

After that, the base station 100 updates the configuration of thedynamic TDD configuration to the configuration signaled in step S164(step S180). At the same time, the dynamic TDD terminal 200 likewisemodifies the configuration of the dynamic TDD configuration to theconfiguration signaled from the base station 100 (step S184). However,the timing of an ACK/NACK associated with the downlink traffic or ULgrant received in step S176 or an uplink transmission is unaffected bythe update of the dynamic TDD configuration.

The dynamic TDD terminal 200 decides the transmission timing of anACK/NACK or uplink traffic on the basis of the configuration numbersignaled from the base station 100 in step S140, and transmits theACK/NACK or uplink traffic to the base station 100 at the decided timing(step S188).

4. CONCLUSION

The foregoing thus describes an embodiment of technology according tothe present disclosure in detail using FIGS. 1 to 14B. According to theembodiment discussed above, the timing of control signaling in a secondlink direction associated with data transmission in a first linkdirection is configured independently of a link direction configurationconfigured for the purpose of radio communication in a time-divisionduplex (TDD) scheme. Consequently, it is possible to prevent loweredthroughput caused by link direction collisions, while also eliminatingthe need for the load-heavy processing of making a link directioncollision judgment every time the link direction configuration isupdated.

In addition, according to the embodiment discussed above, the timing ofthe above control signaling is signaled to a terminal device separatelyfrom the link direction configuration configured according to the UL-DLtraffic ratio. Consequently, a terminal device is able to suitablyascertain and expect the timings of mutually associated datatransmissions and control signaling, irrespectively of link directionconfiguration updates.

In addition, according to the embodiment discussed above, the timing ofthe above control signaling is signaled in a format that specifies onefrom among multiple configuration candidates for the purpose of linkdirection configuration. Consequently, the number of signaled bits maybe only several bits for a configuration number. For this reason, evenif the new signaling described above is adopted, there is only a slightincrease in signaling overhead. Also, the data defining the set ofconfiguration candidates is data also held by legacy terminals. For thisreason, existing data may be reused to easily realize the mechanismdiscussed above, without introducing additional data definitions.

In addition, according to the embodiment discussed above, the timing ofthe above control signaling may be signaled to a terminal device whenthat terminal device connects to a radio communication network.Consequently, even in the case of using a set of configurationcandidates that is unique to a radio communication network, optimalcontrol signaling timings for avoiding lowered throughput may besuitably reported to a terminal device.

Note that the series of control processes conducted by the devicesdescribed in this specification may be realized in any of software,hardware, and a combination of software and hardware. A programconstituting software is stored in advance in a non-transitory mediumprovided internally or externally to each device, for example. Eachprogram is then loaded into random access memory (RAM) at runtime andexecuted by a processor such as a central processing unit (CPU), forexample.

The foregoing thus describes preferred embodiments of the presentdisclosure in detail and with reference to the attached drawings.However, the technical scope of the present disclosure is not limited tosuch examples. It is clear to persons ordinarily skilled in thetechnical field of the present disclosure that various modifications oralterations may occur insofar as they are within the scope of thetechnical ideas stated in the claims, and it is to be understood thatsuch modifications or alterations obviously belong to the technicalscope of the present disclosure.

Additionally, the present technology may also be configured as below.

(1)

A communication control device that controls radio communicationconducted by a terminal device according to a time-division duplex (TDD)scheme on a radio communication network, the communication controldevice including:

a configuration section that configures, for each frame that includes aplurality of subframes, a link direction configuration expressing a linkdirection per subframe for the radio communication,

wherein the configuration section configures a timing of controlsignaling in a second link direction which is associated with datatransmission in a first link direction in the radio communication, andwhich is opposite to the first link direction, independently of theconfigured link direction configuration.

(2)

The communication control device according to (1), further including:

a signaling section that signals, to the terminal device, the linkdirection configuration and the timing configured by the configurationsection.

(3)

The communication control device according to (2), wherein

the configuration section configures the link direction configurationselected from a plurality of configuration candidates for the radiocommunication, and

the signaling section signals the timing by specifying one from amongthe plurality of configuration candidates.

(4)

The communication control device according to (3), wherein

the first link direction is downlink, and the second link direction isuplink, and

the control signaling is an ACK/NACK transmitted from the terminaldevice as a response to a downlink transmission.

(5)

The communication control device according to (3), wherein

the first link direction is uplink, and the second link direction isdownlink, and

the control signaling is an uplink grant transmitted to the terminaldevice prior to an uplink transmission.

(6)

The communication control device according to (4), wherein

the signaling section specifies a candidate with a higher downlink ratiofrom among the plurality of configuration candidates.

(7)

The communication control device according to (5), wherein

the signaling section specifies a candidate with a higher uplink ratiofrom among the plurality of configuration candidates.

(8)

The communication control device according to (6) or (7), furtherincluding:

a storage section that stores a table associating, for eachconfiguration candidate, a timing of the data transmission with a timingof the control signaling,

wherein one of the timing of the data transmission and the timing of thecontrol signaling is decided on the basis of the other timing byreferencing an entry for a specified configuration candidate in thetable.

(9)

The communication control device according to any one of (3) to (8),wherein

the configuration section selects the link direction configuration to beconfigured from the plurality of configuration candidates according to aratio between uplink traffic and downlink traffic on the radiocommunication network.

(10)

The communication control device according to any one of (3) to (9),wherein

the plurality of configuration candidates is unique to the radiocommunication network, and

the signaling section signals the timing to the terminal device when theterminal device connects to the radio communication network.

(11)

The communication control device according to any one of (2) to (10),wherein

the configuration section configures the link direction configurationfor a first terminal group, and configures another link directionconfiguration for a second terminal group, and

the signaling section signals the link direction configuration to aterminal device belonging to the first terminal group on a shorter cyclethan a cycle of signaling to a terminal device belonging to the secondterminal group.

(12)

The communication control device according to any one of (1) to (11),wherein

the communication control device is a base station.

(13)

The communication control device according to any one of (1) to (11),wherein

the communication control device is a control node that communicateswith the terminal device via a base station.

(14)

A communication control method for controlling radio communicationconducted by a terminal device according to a time-division duplex (TDD)scheme on a radio communication network, the communication controlmethod including:

configuring, for each frame that includes a plurality of subframes, alink direction configuration expressing a link direction per subframefor the radio communication; and

configuring a timing of control signaling in a second link directionwhich is associated with data transmission in a first link direction inthe radio communication, and which is opposite to the first linkdirection, independently of the configured link direction configuration.

(15)

A program causing a computer of a communication control device thatcontrols radio communication conducted by a terminal device according toa time-division duplex (TDD) scheme on a radio communication network tofunction as:

a configuration section that configures, for each frame that includes aplurality of subframes, a link direction configuration expressing a linkdirection per subframe for the radio communication,

wherein the configuration section configures a timing of controlsignaling in a second link direction which is associated with datatransmission in a first link direction in the radio communication, andwhich is opposite to the first link direction, independently of theconfigured link direction configuration.

(16)

A terminal device including:

a radio communication section that communicates with a base stationaccording to a time-division duplex (TDD) scheme; and

a control section that, according to a link direction configurationindicated by first signaling from the base station, configures a linkdirection per subframe for each frame that includes a plurality ofsubframes,

wherein the control section configures, on the basis of second signalingfrom the base station, an offset between a timing of a data transmissionin a first link direction and a timing of control signaling in a secondlink direction which is associated with the data transmission, and whichis opposite to the first link direction.

(17)

A radio communication method executed by a terminal device provided witha radio communication section that communicates with a base stationaccording to a time-division duplex (TDD) scheme, the radiocommunication method including:

configuring, according to a link direction configuration indicated byfirst signaling from the base station, a link direction per subframe foreach frame that includes a plurality of subframes; and

configuring, on the basis of second signaling from the base station, anoffset between a timing of a data transmission in a first link directionand a timing of control signaling in a second link direction which isassociated with the data transmission, and which is opposite to thefirst link direction.

(18)

A program causing a computer of a terminal device provided with a radiocommunication section that communicates with a base station according toa time-division duplex (TDD) scheme to function as:

a control section that, according to a link direction configurationindicated by first signaling from the base station, configures a linkdirection per subframe for each frame that includes a plurality ofsubframes,

wherein the control section configures, on the basis of second signalingfrom the base station, an offset between a timing of a data transmissionin a first link direction and a timing of control signaling in a secondlink direction which is associated with the data transmission, and whichis opposite to the first link direction.

(19)

A communication control system including:

a terminal device that communicates with a base station according to atime-division duplex (TDD) scheme; and

a communication control device that controls radio communicationconducted by the terminal device,

the communication control device including

-   -   a configuration section that configures, for each frame that        includes a plurality of subframes, a link direction        configuration expressing a link direction per subframe for the        radio communication,

wherein the configuration section configures a timing of controlsignaling in a second link direction which is associated with datatransmission in a first link direction in the radio communication, andwhich is opposite to the first link direction, independently of theconfigured link direction configuration.

REFERENCE SIGNS LIST

-   1 communication control system-   100 communication control device-   140 configuration section-   142 storage section-   150 signaling section-   104 terminal device (legacy terminal)-   200 terminal device (dynamic TDD terminal)-   210 radio communication section-   230 control section

1. A communication control device that controls radio communicationconducted by a terminal device according to a time-division duplex (TDD)scheme on a radio communication network, the communication controldevice comprising: a configuration section that configures, for eachframe that includes a plurality of subframes, a link directionconfiguration expressing a link direction per subframe for the radiocommunication, wherein the configuration section configures a timing ofcontrol signaling in a second link direction which is associated withdata transmission in a first link direction in the radio communication,and which is opposite to the first link direction, independently of theconfigured link direction configuration.
 2. The communication controldevice according to claim 1, further comprising: a signaling sectionthat signals, to the terminal device, the link direction configurationand the timing configured by the configuration section.
 3. Thecommunication control device according to claim 2, wherein theconfiguration section configures the link direction configurationselected from a plurality of configuration candidates for the radiocommunication, and the signaling section signals the timing byspecifying one from among the plurality of configuration candidates. 4.The communication control device according to claim 3, wherein the firstlink direction is downlink, and the second link direction is uplink, andthe control signaling is an ACK/NACK transmitted from the terminaldevice as a response to a downlink transmission.
 5. The communicationcontrol device according to claim 3, wherein the first link direction isuplink, and the second link direction is downlink, and the controlsignaling is an uplink grant transmitted to the terminal device prior toan uplink transmission.
 6. The communication control device according toclaim 4, wherein the signaling section specifies a candidate with ahigher downlink ratio from among the plurality of configurationcandidates.
 7. The communication control device according to claim 5,wherein the signaling section specifies a candidate with a higher uplinkratio from among the plurality of configuration candidates.
 8. Thecommunication control device according to claim 6, further comprising: astorage section that stores a table associating, for each configurationcandidate, a timing of the data transmission with a timing of thecontrol signaling, wherein one of the timing of the data transmissionand the timing of the control signaling is decided on the basis of theother timing by referencing an entry for a specified configurationcandidate in the table.
 9. The communication control device according toclaim 3, wherein the configuration section selects the link directionconfiguration to be configured from the plurality of configurationcandidates according to a ratio between uplink traffic and downlinktraffic on the radio communication network.
 10. The communicationcontrol device according to claim 3, wherein the plurality ofconfiguration candidates is unique to the radio communication network,and the signaling section signals the timing to the terminal device whenthe terminal device connects to the radio communication network.
 11. Thecommunication control device according to claim 2, wherein theconfiguration section configures the link direction configuration for afirst terminal group, and configures another link directionconfiguration for a second terminal group, and the signaling sectionsignals the link direction configuration to a terminal device belongingto the first terminal group on a shorter cycle than a cycle of signalingto a terminal device belonging to the second terminal group.
 12. Thecommunication control device according to claim 1, wherein thecommunication control device is a base station.
 13. The communicationcontrol device according to claim 1, wherein the communication controldevice is a control node that communicates with the terminal device viaa base station.
 14. A communication control method for controlling radiocommunication conducted by a terminal device according to atime-division duplex (TDD) scheme on a radio communication network, thecommunication control method comprising: configuring, for each framethat includes a plurality of subframes, a link direction configurationexpressing a link direction per subframe for the radio communication;and configuring a timing of control signaling in a second link directionwhich is associated with data transmission in a first link direction inthe radio communication, and which is opposite to the first linkdirection, independently of the configured link direction configuration.15. A program causing a computer of a communication control device thatcontrols radio communication conducted by a terminal device according toa time-division duplex (TDD) scheme on a radio communication network tofunction as: a configuration section that configures, for each framethat includes a plurality of subframes, a link direction configurationexpressing a link direction per subframe for the radio communication,wherein the configuration section configures a timing of controlsignaling in a second link direction which is associated with datatransmission in a first link direction in the radio communication, andwhich is opposite to the first link direction, independently of theconfigured link direction configuration.
 16. A terminal devicecomprising: a radio communication section that communicates with a basestation according to a time-division duplex (TDD) scheme; and a controlsection that, according to a link direction configuration indicated byfirst signaling from the base station, configures a link direction persubframe for each frame that includes a plurality of subframes, whereinthe control section configures, on the basis of second signaling fromthe base station, an offset between a timing of a data transmission in afirst link direction and a timing of control signaling in a second linkdirection which is associated with the data transmission, and which isopposite to the first link direction.
 17. A radio communication methodexecuted by a terminal device provided with a radio communicationsection that communicates with a base station according to atime-division duplex (TDD) scheme, the radio communication methodcomprising: configuring, according to a link direction configurationindicated by first signaling from the base station, a link direction persubframe for each frame that includes a plurality of subframes; andconfiguring, on the basis of second signaling from the base station, anoffset between a timing of a data transmission in a first link directionand a timing of control signaling in a second link direction which isassociated with the data transmission, and which is opposite to thefirst link direction.
 18. A program causing a computer of a terminaldevice provided with a radio communication section that communicateswith a base station according to a time-division duplex (TDD) scheme tofunction as: a control section that, according to a link directionconfiguration indicated by first signaling from the base station,configures a link direction per subframe for each frame that includes aplurality of subframes, wherein the control section configures, on thebasis of second signaling from the base station, an offset between atiming of a data transmission in a first link direction and a timing ofcontrol signaling in a second link direction which is associated withthe data transmission, and which is opposite to the first linkdirection.
 19. A communication control system comprising: a terminaldevice that communicates with a base station according to atime-division duplex (TDD) scheme; and a communication control devicethat controls radio communication conducted by the terminal device, thecommunication control device including a configuration section thatconfigures, for each frame that includes a plurality of subframes, alink direction configuration expressing a link direction per subframefor the radio communication, wherein the configuration sectionconfigures a timing of control signaling in a second link directionwhich is associated with data transmission in a first link direction inthe radio communication, and which is opposite to the first linkdirection, independently of the configured link direction configuration.